Datasheet

t = 0.5 ms / div
OUTPUT VOLTAGE = 5.0V/div
CAPACITOR VOLTAGE = 1.0V/div
R1 = R2 = 4.8kΩ, C1= 0.1µF, R = 1kΩ
L
Figure 14
C
(µF)
10
1.0
0.1
0.01
0.001
0.1 1 10 100 1k 10k f (Hz)
o
1
M
Ω
R
1
+
R
2
=
1
0M
Ω
1
0
0
k
Ω
1
0
k
Ω
1
k
Ω
Figure 15 : Free Running Frequency versus R
1
,
R
2
andC
1
Figure 14 showsactualwaveformsgeneratedin this
mode of operation.
The charge time (output HIGH) is given by :
t
1
= 0.693 (R
1
+R
2
)C
1
and the discharge time (outputLOW) by :
t
2
= 0.693 (R
2
)C
1
Thus the total period T is given by :
T=t
1
+t
2
= 0.693 (R
1
+2R
2
)C
1
The frequency ofoscillation is them :
f =
1
T
=
1.44
(R
1
+ 2R
2
) C
1
and may be easily found by figure 15.
The duty cycle is given by :
D =
R
2
R
1
+ 2R
2
Output
3
48
7
5
1
R1
C1
2
6
R2
Control
Voltage
NE555
V
CC
= 5 to 15V
0.01
µF
Figure 13
PULSE WIDTH MODULATOR
When the timer is connected in the monostable
mode and triggered with a continuous pulse train,
theoutputpulse width can be modulatedby a signal
applied to pin 5. Figure 16 shows the circuit.
Trigger
Output
R
C
NE555
2
4
3
1
5
6
7
Modulation
Input
8
A
V
CC
Figure 16 : Pulse Width Modulator.
NE555/SA555/SE555
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